Validation of AJCC TNM staging for breast tumors diagnosed before 2004 in cancer registries

Purpose American Joint Committee on Cancer (AJCC) Tumor (T), Nodal (N), and Metastatic (M) staging is commonly used in clinical practice for treatment decisions, yet before 2004, Surveillance Epidemiology and End Results (SEER)-affiliated cancer registries did not routinely include TNM staging defined by AJCC criteria, reporting instead SEER Summary Staging.